Summary: In the process of constructing a map of the pneumococcus chromosome by transformation, a search for linkage groups involving the markers ery-r2, str-r41, amiA-r1, opt-r2 and tet-A has been carried out. No linkage was found amongst the first four markers, but linkage was found between ery-r2 and tet-A. The discrepancy between these results and the previously reported linkage between the loci conferring resistance to erythromycin and streptomycin is discussed. The anomalous position of the ery-r2-tet-A linkage in relation to the chromosome map obtained by the density-shift method, and the implications to the mode of replication of the chromosome, are discussed. Two models are proposed for the replication of the pneumococcal chromosome.